Abrasive articles and methods of making the same



April 19, 1966 E. HURST 3,246,430

ABRASIVE ARTICLES AND METHODS OF MAKING THE SAME Filed April 25, 1965 4 Sheets-Sheet 1 INVENTOR.

EDWARD HURST ATTORNEY April 19, 1966 E. HURST 3,246,430

ABRASIVE ARTICLES AND METHODS OF MAKING THE SAME Filed April 25, 1963 4 Sheets-Sheet 2 INVENTOR. EDWARD HURST ATTORNEY April 19, 1966 u s 3,246,430

ABRASIVE ARTICLES AND METHODS OF MAKING THE SAME Filed April 25, 1963 4 Sheets-Sheet 8 INVENTOR. EDWARD HURST /KQWM ATTORNEY E. HURST April 19, 1966 ABRASIVE ARTICLES AND METHODS OF MAKING THE SAME Filed April 25, 1963 4 Sheets-Sheet 4 Fig. 9

INVENTOR. EDWARD HURST ATTORNEY United States Patent 3,246,430 ABRASIVE ARTICLES AND METHODS OF MAKING THE SAME Edward Hurst, Duxbury, Mass., assignor to Rexall Drug and Chemical Company, Los Angeles, Calif., a corporation of Delaware Filed, Apr. 25, 1963, Ser. No. 275,759 1 Claim. (Cl. 51-402) This invention relates to abrasive articles and to methods for their manufacture. More particularly it relates toabrasive articles such as abrasive discs, belts, wheels and the like comprising a fibrous abrasive-containing matrixto which is secured an abrading body having a working face with a multiplicity of cutting areas interrupted by depressed clearance areas which are selfdischarging in character.

In abrasive coated products wherein the abrasive grain coating is substantially uniform and rather closely packed, there is a normal tendency of the grain coating to fill or load with abraded material and detritus, ie the loosened abrasive particles, during use. The abrading surfaces soon become clogged or gummed by the fine grit and minute particles worn from the abrading surface and from the material being adraded. These fine particles must rub completely across the face of the work before they can find release. The particles form a coating or film between the face of the work and the abrading surface and prevent the necessary free and intimate cutting or grinding contact between the abrading surface and the work. This loading results in a loss of abrading efiiciency and, also, provides an uneven surface on the abrasive sheet which may produce an uneven surface on the article being abraded.

Theproblems of reducing the amount of loading and glazing of the abrasive article have in the past been recognized in the art and various attempts have been made to correct the difiiculty. However, the previous attempts to solve the problem have not been altogether satisfactory in practical use and in the practical manufacture of such abrading articles. For example, one proposed remedy has been'the use of a multiplicity of blank or clearance spaces surroundingindividual isolated projecting portions or spots of abrading material on the face of an abrasive disc, such as in US. Patent 2,907,146. However, such a construction requires the use of a heavy coating of abrasive material and. yields a stiif and unwieldy abrasive disc. Because of the limited bonding capacity of the base material, any flexing of the disc during use cracks and breaks the abrasive coating. Furthermore, during use, the isolated abrasive spots on such abrasive articles shear or break off, thereby greatly reducing. the, life expectancy of sucharticles. Another proposed remedy'hasbeen the use .of a base sheet having numerous openings through which the detritus can pass, such as U.S.' Patent 2,838,890. However, such abrasive articles suffer from the disadvantage that they are difficult and expensive to fabricate, and the grit and detritus must still rub across the face of the work for a considerable distance before they can find release. Also, the use of such a perforated base sheet tends to weaken the abrasive sheet, resulting in sharing and tearing of the sheet during use. Similarly, other previously devised means have not been satisfactory for various reasons, and the present invention is the result of further pressed clearance spaces.

3,246,430 Patented Apr. 19, 1966 efforts to provide a more satisfactory solution to the foregoing and other problems relating to abrasive coated articles.

It is therefore an object of this invention to provide an improved abrasive articlewhich is fast cutting, flexible and which includes means for preventing the loading and glazing of the article withabraded material during use.

Another object of the invention is to provide an abrading surface of such formation and construction so as to eliminate glazing and loading of the surface and thereby increase the effective working life of the-surface and lthe cutting or abrading speed of such surface.

Another object of the invention is to provide an abrasive article so constructed that the amount of contact area between the abrasive article and the work piece is diminished so as to make the article cut more effectively and which is also provided with suitable clearance spaces so that the detritus may be thrown off and there will be substantially no loading or glazing of the disc under conditions of use.

It is a further object .to provide abrasive articles composed of abrasive-included fibrous material having a patterned or confi-gurated abrading surface composed of a continuous network of bonded abrasive grain forming interconnected abrasive ridges separated by depressed clearance spaces.

It is a still further object of the invention to provide abrasive articles of the aforesaid type which will not only perform efficiently in grinding and/or polishing operations with a minimum of loading but will be further characterized by a self-discharging or non-loading ability.

Various other objects and advantages will appear from the following description of several embodiments of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claim.

In accordance with the present invention, abrasive articles such as grinding and polishing wheels, abrasive discs and belts, set-up wheels, bufling wheels and devices and similar types of abrasive articles composed of an abrasive included fibrous material and usually reinforced by one or more layers of reinforcing fabric to enhance the mechanical strength of the finished article, are provided with a patterned or configurated abrading surface whereby the abrasive characteristics of the article are enhanced and the tendency of the article to. load with detritus is minimized. The abrading surface of the article, instead of being a completely coated, unbroken surface, is made of a multiplicity of interconnected, raised .cutting surfaces inteispatial with depressed areas or blank or non-working spots. These depressed areas or blank spots provide ample clearance for grinding detritus which tends to be ejected from the clearance spaces by the action of the disc in use since the multiplicity of clearance areas are such that the disc is relatively highly flexible and the flexing action'of the discas it is presented to the workpiece and as it leaves the workpiece serves to free the clearance spaces from any detritus which is lodged there in the course of grinding.

Abrasive articles made in accordance with this invention are non-glazing for the grit and detritus will only rub across a few abrasive grains on the surface of the raised abrasive ridges before finding release into the de- Thus, each abrasive grain is presented in such a way as to be able to perform its cutting action with optimum freedom from interference by adjacent abrasive particles or material removed from the workpiece.

The abrasive articles of the present invention, irrespective of the specific form in which they are made are composed of a matrix or reticulum of a flexible, resilient, abrasive-included fibrous sheet material. This material is a non-lamellar web structure of individual cardzuble interlocked fibers, adhesive binder and abrasive granules which are distributed internally of and throughout the fibrous web and are firmly anchored in position by being surrounded by the long fibers. Although the uppermost granules penetrate through and above the surface of the Web, they are securely attached by the surrounding fibers, which with the aid of the adhesive binder anchors them in position. On one surface of the matrix is distributed a continuous network of resin-bonded abrasive grain forming a continuous network of interconnected abrasive ridges of substantial depth surrounding depressed or clearance areas. The network of abrasive ridges consists of abrasive grain in depth in longitudinal ridges and transverse ridges normal to the longitudinal ridges. A suitable flexible support or backing, such as rubber-sized or latexsized canvas or duck is utilized as a backing on the opposite surface of the matrix to enhance the mechanical strength of the finished abrasive article. According to one modification of the invention the matrix may be reinforced by a network of filamentary material, such as nylon or glass strands.

In order to better understand the nature of the herein described articles and methods of making the same, reference is made to the accompanying drawings showing specific examples of abrasive articles made in accordance with the present invention, and in which FIGURE 1 is a plan view of a portion of an abrasive disc made in accordance with the present invention in which the abrasive included matrix has been molded into an indented latticed or wafile pattern to form a series of elevated portions completely surrounded by a continuous network of interconnected channels or troughs;

FIGURE 2 is an enlarged cross-sectional view through the line 22 of FIGURE 1, depicting the nature of the elevated portions and the troughs of the matrix;

FIGURE 3 is a view similar to that of FIGURE 1 in which the interconnected troughs have been filled with resin-coated abrasive grain;

FIGURE 4 is an enlarged cross-sectional view through the line 4-4 of FIGURE 3;

FIGURE 5 is a view similar to that of FIGURE 3 after the article has been subjected to a pressing operation;

FIGURE 6 is a cross-sectional view through the line 66 of FIGURE 5;

FIGURE 7 is a plan view of an enlarged portion of the pressed article shown in FIGURE 5;

FIGURE 8 is a plan view of an abrasive disc made in accordance with the present invention;

FIGURE 9 is a perspective view of an endless abrasive belt made in accordance with the present invention.

In accordance with the present invention an abrasiveincluded fibrous matrix suitable for use as a supporting and carrier means for abrasive grain can be made according to my U.S. Patent No. 2,284,739. In this process a web of a plurality of carded fibrous membranes is formed by interlocking said membranes together to form a strong non-lamellar Web structure. Abrasive grain and a suitable adhesive agent are incorporated internally of said fibrous web, the abrasive particles extending from the interior to the surface and projecting therefrom. Any of the abrasive materials in common use may be employed in forming the matrix and the size of the abrasive particles may vary from the finest polishing powders to the largest grains.

The carded membranes are formed of webs of loosely adhering independent fibers and may consist of any animal, vegetable, mineral or synthetic fibrous material capable of being carded into web form. Cotton fibers have been found to be highly satisfactory.

In addition, various modifying agents, such as waterproofing compounds, anti-friction agents, fiexibilizers and other fillers may be incorporated in the web to impart specific properties thereto.

The choice of a particular adhesive to be used as the bonding medium in the fibrous matrix is dependent upon the particular requirements of the final abrasive product. While adhesives such as latex, animal glue, synthetic or natural rubber binders, sodium silicate, or resinous adhesives can be used, for the purposes of the present inven tion it has been found highly satisfactory to use a resilient permanently thermoplastic resinous polymerization product, such as thermoplastic resinous polymers, copolymers and heteropolymers of acrylic acids, as the interstitial bonding medium for the inter-locked fibers and abrasive granules. Such a binder is preferred because it is of a permanently tough resilient character. Suitable acrylic polymers are disclosed in my U.S. Patent No. 3,048,482, however, other resilient, thermoplastic resinous materials comparable to the acrylic resins can be used as the binder of the matrix.

The abrasive grains to be used in forming the abrading surface of the abrasive article, prior to their application to the surface of the matrix, are first coated with a heat-hardenable, permanently rigid, organic bond such as a heat-hardenable phenol formaldehyde-resinous condensation product or a vulcanizable hard rubber, and dried to give a mass of individually separate abrasive grains, coated with a non-tacky film of organic bonding material. In this condition the grains may be handled and stored the same as ordinary uncoated abrasive grain. The coated grains are firm and noncoherent and yet are sufficiently soluble and fusible so that they are readily made adherent to a backing material. Suitable compositions for coating the abrasive grain are well known in the abrasive art, for example the following US. patents disclose suitable compositions for such use, 1,626,246; 1,953,984; 2,010,873; 2,076,517; 2,171,635 and 2,201,321. After the coated abrasive grains have been prepared, they are applied to the matrix and subjected to heat and pressure in a manner described below.

Instead of coating the abrasive grain with the heathardenable, organic bond in a separate operation and then transferring the coated grain to the molded sheet material, a composition of abrasive grain and the organic bond may be charged to the longitudinal and transverse troughs of the molded matrix and the assembly then subjected to heat and pressure.

Abrasive articles of the above-described type having an abrading surface composed of a continuous network of resin bonded abrasive grain forming interconnected abrasive ridges separated by depressed clearance spaces have been satisfactorily made as follows. A fibrous matrix of interlocked textile fibers having individual abrasive granules distributed substantially uniformly therein is prepared as discussed above in accordance with U.S. Patent No. 2,284,738. This sheet material is then subjected to a molding operation, such as by passing it through a set of configurated rollers or subjecting it to pressure between mold plates of suitable design, to form an embossed wafile pattern in the material in the form of a multiplicity of elevated portions or mounds, extending in from one side of the sheet, separated by troughs or channels. Referring to the drawing, FIGURE 1, numeral 11 illustrates a portion of the fibrous, abrasive included matrix 12, which has been subjected to such a molding operation. As can be seen in the drawing, the molding operation forms in the sheet material a multiplicity of isolated elevated portions or mounds 13, separated by longitudinal troughs 14 and transverse troughs 14', normal to and intersecting the longitudinal troughs. The molding operation thereby forms a sheet material having an interconnected network of troughs spaced apart by the elevated portions. Numeral 15 designates abrasive granules included-inthe fibrous sheetmaterial or matrix projecting above the surface ofthe sheet material. The nature of the troughs and elevated portions can be more clearly seen in FIGURE 2, which-is a cross-sectional view of the sheet material taken along lines 2-2 of FIGURE 1.

The molded sheet material is then cut into the desired.

size and shape for making abrasive articles of the selected form and type. For example, if abrasive discs are to be made the sheet material is cut or died out in the form of discs of a diameter equal to the diameter of the desired disc.

The longitudinal and transverse troughs or channels 14 and 14' of the molded sheet material are then filled with the abrasive grain-organic bond composition prepared in the manner described above. As shown in FIGURE 3, the abrasive grain-organic bond composition 16 completely fills the troughs to a depth substantially equal to the upper surface of the elevated portions 13, as shown in FIGURE 4. The depth of the coated abrasive grain 16 in the troughs 14 and 14' may of course be varied as desired. The abrasive-filled matrix is then placed on one or more layers of suitable flexible backing material 17, such as latex-filled fabric, cut to the same size and shape as the abrasive filled sheet material, so that the abrasivefilled troughs face upwardly, as shown in FIGURE 4. The abrasive-charged sheet material and backing material are then placed in a mold so that the backing material rests -on the bottom plate of the mold, and the top mold plate having a surface of a compressible material such as vulcanized rubber is then placed over the assembled materials. The entire assembly is then subjected to heat and pressure for a period of time suflicient to polymerize or vulcanize the resin or other organic bond of the coated abrasive granules, mature the thermoplastic resin of the fibrous sheet material and combine the backing and sheet material to form the resultant abrasive article. The application of heat and pressure causes the resin coating on the abrasive grain to flow from the upper surfaces of the grains so that substantially all of the resin is thereby made available as a bond for the grains and for attaching the grains to the backing. The temperature, pressure and time factors in the pressing operation are critical only to the extent that they must be sufficient to polymerize or vulcanize the coating on the abrasive granules, mature the thermoplastic resin and combine the backing and sheet material. Pressure in the range from about 200 psi. to 5000 p.s.i. or more may be used, but a more preferred range is from about 250 psi. to 2500 p.s.i. Suitable temperatures for this step are in the range of about 250-350 F., and the time of pressing should be about to 20 minutes. It will be readily apparent, however, that the temperature, pressure and time factors may be varied over wide ranges without adversely affecting the abrasive article, and will, to some extent, be dependent on the thickness of the article being pressed.

The pressing operation not only polymerizes the coating on the abrasive grain but also compacts the loose abrasive grain into a dense, compact, rigid bonded mass embedded in the fibrous matrix and depresses the elevated portions 13 of the matrix as shown in FIGURES 5-7. Thus, as a result of the application of heat and pressure to the abrasive filled matrix, the elevated portions 13 of the matrix are leveled to form depressed clearance areas 18 between the abrasive ridges 16 and 16'. Also, the application of heat to the fibrous matrix causes the thermoplastic resinous binder to become softened so that the application of pressure on the coated abrasive grain not only compacts the grain but causes the abrasive grain to become embedded within the matrix, as can be seen in FIGURE 6.

FIGURE 8 shows a completed abrasive disc 20, made in accordance with the present invention with a central mounting arbor 21, in which the abrading face of the disc is composed of a continuous network of resin bonded abrasive'grain forming interconnected longitudinal abra-' sive ridges 16 and transverse abrasive ridges 16' normal to and intersecting the longitudinal ridges, the abrasive ridges being separated by depressed clearance spaces 18.

FIGURE 9 depicts an endless abrasive belt 22 embodying the same structural features as the abrasive disc.

In abrasive discs made in accordance with this invention, the contact area of the disc is cut down so as to produce a higher unit pressure on the cutting edges of the abrasive particles and to effect a faster rate of cutting.

While the disc shown illustrates clearly one specific embodiment of abrasive discs which can be made in accordance with the present invention, it is readily apparent that numerous variations in such abrasive articles are possible without departing from the principles involved. For example, the depth of the troughs or channels may vary depending upon the type of article being made and the purpose for which it is intended. Thus, increasing the depth of the troughs tends to promote flexibility of the resulting article. If an abrasive disc having more vigorous grinding action and stiffer operating properties is desired the fibrous matrix is molded so that the troughs are shallower in depth and have a greater width.

Also, during the formation of the abrasive included fibrous sheet material a reinforcing network of filamentary reinforcing strands of nylon yarn, glass yarn or other reinforcements may be incorporated into the fibrous web. When the molding operation is carried out the elevated portions formed in the material will be in register with the interstices formed by the network of reinforcing filaments.

Any of the abrasive materials in common use may be employed in forming the abrading surface of articles made in accordance with the present invention. Such materials include silicon carbide, aluminum oxide, flint, corundum, emery and similar substances. The size of the abrasive grain may vary from the finest polishing or buffing powders to the coarser grit sizes used in grinding.

Any suitable flexible material can be used as the backing such as one or more layers of latex-filled fabric, canvas, duck or other flexible material, the fibers of any of said fabrics being any material or synthetic, organic or inorganic textile fibrous material, such as glass or ceramic shape, form or function of the article constitutes an abralulose fibers and the like, singly or in blends.

Thus, it is readily apparent that the present invention provides an abrasive article which can be made in many forms but which in every case regardless of the specific shape, vform or function of the aifticle constitutes an abrasive-included fibrous body of material having a working face comprising a continuous network of bonded abrasive grain forming interconnected abrasive ridges separated by depressed clearance spaces.

It will be understood that various changes in the details, materials, steps and arrangement of parts, which have herein been described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claim.

What is claimed is:

A flexible self-clearing abrasive article comprising a flexible backing, an abrasive-included fibrous matrix of interlocked fibers having an interstitial bonding medium of a resilient, permanently thermoplastic resin bonded to said backing, and a Working surface formed by a continuous network of abrasive ridges the inner portions of which are embedded in said matrix and the outer portions of which project from said matrix, said ridges consisting of abrasive grain compacted and bonded into a dense mass having a reverse pyramidal cross section, said continuous network of abrasive ridges consisting of a multiplicity of parallel longitudinal ridges in spaced relationship and a multiplicity of parallel transverse ridges in spaced relationship normal to and, at their intersections, integral with said longitudinal ridges, thereby defining open clearance areas 7 8 between said ridges which are depressed in relation to the 2,584,862 2/ 1952 Garrison 51-295 upper portions of said ridges. 2,770,928 11/1956 Van Ormer et a1. 51-195 2,804,733 9/ 1957 Hurst 51397 References Cited y the Examiner 2,907,146 10/1959 Dyar 51-195 UNITED STATES PATENTS 5" 82 8/1962 Hurst 51-297 X 816,461 3/1906 Gorton 51--395 2,125,782 8/1938 Heald 51 295v ROBERT C. RIORDON, Przmary Exammer.

2,284,716 6/1942 Benner et a1. 51-297 LESTER M-SWINGLEExaminer- 

